Genetically predisposed individuals, who make up about 10% of the population, become hypersensitized (allergic) to antigens from a variety of environmental sources to which they are exposed. Those antigens that can induce immediate and/or delayed types of hypersensitivity in people are called allergens. King, T. P., Adv. Immun. 23:77-105(1976). The symptoms of hay fever, asthma and hives are forms of allergy which can be caused by a variety of allergens, such as products of grasses, trees, weeds, animal dander, insects, food, drugs and chemicals. The antibodies involved in allergy belong primarily to the immunoglobulin E (IgE) class of immunoglobins. IgE binds to mast cells and basophils. Upon combination of a specific allergen with IgE bound to mast cells, the IgE is cross-linked on the cell surface, resulting in the physiological effects of IgE-antigen interaction. Degranulation results in release of, among other substances, histamine, heparin, chemotactic factor for eosinophils and the leukotrienes, C4, D4 and E4, which cause prolonged constriction of bronchial smooth muscle cells. Hood, L. E. et al., Immunology (2nd ed.), pp. 460-462, The Benjamin/Cumming Publishing Co., Inc. (1984). These released substances are the mediators which result in allergic symptoms caused by combination of IgE with a specific allergen. Through them, the effects of an allergen are manifested. Such effects may be systemic or local in nature, depending on the route by which the antigen entered the body and the pattern of deposition of IgE and mast cells. Local manifestations generally occur on epithelial surfaces at the location at which the allergen entered the body. Systemic effects can include anaphylaxis (anaphylactic shock), which is the result of an IgE-basophil response to circulating (intravascular) antigen.
It has been estimated that there are approximately 10 million cat allergic individuals in the United States. Ohman, J. L. and Sundin, B., Clin. Rev. Allergy, 5:37-47 (1987). An allergen of particular concern for many people is the feline skin and salivary gland allergen of the domestic cat Felis domesticus allergen I (Fel d I), also referred to as allergen I, cat 1 and antigen 4. Fel d I has been described as an acidic non-covalently linked homodimer of approximately 39,000 molecular weight on size exclusion HPLC, and 17,000 under nonreducing conditions on gel electrophoresis. Chapman, M. D. et al., J. Immunology, 140(3):812-818 (1988). Chapman and co-workers also describe a single step procedure for the purification of Fel d I from crude house dust extract with a high Fel d I content (50 U/ml) using monoclonal antibody affinity chromatography. In addition, they determined the amino acid composition and partial amino acid sequence of Fel d I. Fel d I has also been described as a 35,000 molecular weight dimer of two noncovalently linked 18,000 molecular weight subunits, which occurs in three isoallergenic forms (pl 3.5 to 4.1 ). Ohman, J. L. et al., J. Allergy Clin. Immunol., 52:231 (1973); Ohman, J. L. et al., J. Immunol, 113:1668 (1974); Leiterman, K. and Ohman, J. L., J. Allergy Clin. Immunol., 74:147 (1984).
Exposure to cat allergen can occur as a result of exposure to the animal or contact with house dust which contains cat allergens. These allergens have been examined in saliva, skin scrapings, cat wash, serum, salivary glands, cat hair, cat dandruff and house dust.
Current desensitization therapy involves treatment with a complex, poorly-defined animal dander extract which often causes adverse effects in individuals to whom it is administered.